Regulation of Cell-Mediated Immunologic Reactivity to Moloney Murine Sarcoma Virus-Induced Tumors. I. Cell and Serum Activity Detected by Leukocyte Adherence Inhibition2, 3

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Abstract
Cell-mediated immunity and serum regulatory factors were studied in an in vitro system involving a spontaneously regressing, virus-induced tumor. Inbred BALB/c and CBA mice were inoculated with Moloney murine sarcoma virus and their peritoneal cells were tested for reactivity in leukocyte-adherence inhibition tests with extracts of syngeneic tumors. Sera from inoculated mice were tested for their effect on this reactivity. At the optimal dilution, tumor extracts induced significant reactions with cells from tumor-bearing mice (progressors) and from mice with regressed tumors (regressors); cells from normal mice and from mice with transplanted, chemically induced tumors were unaffected. Sera from progressor mice specifically blocked the reactivity of syngeneic cells. At the time of maximal tumor development, this blocking activity disappeared and the serum became unblocking; i.e., the regressor serum neutralized the blocking factor in progressor serum. The blocking and unblocking factors were tumor-specific; no cross-reactivity occurred with similar factors related to the chemically induced tumor. Normal cells were not significantly affected by exposure to blocking and unblocking sera. The development of cellular immune reactivity and serum factors detected in vitro corresponded to the cycle of tumor progression and regression observed in vivo.

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